Macroscopic quantum measurements of noncommuting observables

Authors:Tomer Jack Barnea, Marc-Olivier Renou, Florian Fröwis, Nicolas Gisin
Journal:Phys. Rev. A 96, 012111 (2017)
DOI:http://dx.doi.org/10.1103/PhysRevA.96.012111
Abstract:Assuming a well-behaving quantum-to-classical transition, measuring large quantum systems should be highly informative with low measurement-induced disturbance, while the coupling between system and measurement apparatus is fairly simple and weak. Here, we show that this is indeed possible within the formalism of quantum mechanics. We discuss an example of estimating the collective magnetization of a spin ensemble by simultaneous measuring three orthogonal spin directions. For the task of estimating the direction of a spin-coherent state, we find that the average guessing fidelity and the system disturbance are nonmonotonic functions of the coupling strength. Strikingly, we discover an intermediate regime for the coupling strength where the guessing fidelity is quasioptimal, while the measured state is almost not disturbed.
File:barnea2017a.pdf

BibTeX Source

@article{PhysRevA.96.012111,
  title = {Macroscopic quantum measurements of noncommuting observables},
  author = {Barnea, Tomer Jack and Renou, Marc-Olivier and Fr\"owis, Florian and Gisin, Nicolas},
  journal = {Phys. Rev. A},
  volume = {96},
  issue = {1},
  pages = {012111},
  numpages = {5},
  year = {2017},
  month = {Jul},
  publisher = {American Physical Society},
  doi = {10.1103/PhysRevA.96.012111},
  url = {https://link.aps.org/doi/10.1103/PhysRevA.96.012111},
abstract={Assuming a well-behaving quantum-to-classical transition, measuring large quantum systems should be highly informative with low measurement-induced disturbance, while the coupling between system and measurement apparatus is fairly simple and weak. Here, we show that this is indeed possible within the formalism of quantum mechanics. We discuss an example of estimating the collective magnetization of a spin ensemble by simultaneous measuring three orthogonal spin directions. For the task of estimating the direction of a spin-coherent state, we find that the average guessing fidelity and the system disturbance are nonmonotonic functions of the coupling strength. Strikingly, we discover an intermediate regime for the coupling strength where the guessing fidelity is quasioptimal, while the measured state is almost not disturbed.}
}